1. Field of the Invention
The invention concerns a 3D integrated guiding structure and, more particularly, a structure made of a semiconductor material as well as the method of its manufacture.
2. Description of the Prior Art
The making of guides with inter-guide coupling calls for a degree of precision that is difficult to obtain in known techniques owing to the limitations of microlithography techniques.
The invention enables the making of optic guides in which it is possible to achieve precise adjustment of the distance of the guides in the coupling zones.
Furthermore, at the present time, semiconductors have great potential as basic materials for the making of optoelectronic components. The growth techniques (MOCVD or MBE) used enable the thicknesses to be controlled to within a few angstroms, and enable the growth of different types of semiconductors on the same substrate. The interfaces between two different semiconductor layers may be abrupt and of very high crystallographic quality, inducing very low optic losses. At present, the propagation losses are smaller than 0.2 dB/cm (Cf. Y. Bourbin et al, Very Low Loss Waveguides And Efficient Modulators In InGaAsP/InP, Proceedings of the IGWO Conference in Boston, U.S.A., February 1989, pp. 110-112).
Furthermore, at the present time, the techniques of microlithography and the processes of selective chemical attack enable the making of micron-sized patterns. Selective chemical attack is controlled by means of a barrier layer, and it is common to make strips with a thickness of some tens of angstroms and a width of about one micron on a length of several centimeters.
Thus, the association of these two techniques currently enables the making of the structure described in the present invention.
The state of the art of optoelectronic components enables the setting up of functions that can be fulfilled by the structure described in the invention. However, the promising nature of the invention lies in the compactness, the performance characteristics and the multifunctional character of the structure and its very simple method of manufacture.
The invention provides a solution to the problem of 3D integration for it makes use of the vertical dimension. The idea is to use the coupling of light vertically in a bimodal structure and to use the processes of lithography for the two plane dimensions.
The multifunctional character arises from the properties of the directional couplers with the particular feature, in the case of this structure, of having very short coupling lengths. This is a major advantage for wavelength multiplexing or demultiplexing. By contrast, for the light modulation, the effects may be boosted by the presence, in the structure, of highly active materials such as multiple quantum wells (MQW).
The structure of the invention therefore has the following advantages:
3D integration; PA1 Multifunctional character; PA1 Performance characteristics; PA1 Easy manufacture; PA1 Simplicity.